1. Field of the Invention
The present invention relates to a method of manufacturing a waterproof structure for an electric wire drawout portion and, more particularly, to a structure for waterproofing an electric wire drawout portion of a wiring accessory such as a waterproof connector, an electric connection box or the like by means of a rubber-like elastic member and a method of manufacturing such the structure.
2. Description of Relevant Art
In FIGS. 1A and 1B through 4, a conventional example of a waterproof structure for an electric drawout portion of a waterproof connector is shown.
A waterproof structure shown in FIGS. 1A and 1B is of a type wherein in a state where electric wires 7 are clamped by two split upper and lower rubber plugs 30 shown in FIG. 1A and fitted in grooves 31 of the rubber plugs 30 and the resulting rubber plugs 30 are forcedly inserted into a concave portion 32 of a housing 2 of the connector as shown in FIG. 1B (see Japanese Utility Model Application Laid-Open Publication No. 50-54591).
Also, a waterproof structure shown in FIGS. 2A and 2B is of a type wherein holders 33 are freely slidably mounted on a housing of the connector as shown in FIG. 2A and packings 34 are pressed by the holders 33 from above and below electric wires 7 as shown in FIG. 2B (see Japanese Utility Model Application Laid-Open Publication No. 5-57772).
Further, there is also known a waterproof structure wherein as shown in FIG. 3A electric wires 7 are clamped by two split rubber plugs 36 and the rubber plugs 36 are clamped by similarly two split resin-made housings 2 and 2, whereby the housings 2 and 2 are welded to each other by ultrasonic waves being oscillated by an ultrasonic horn 22 with a load being applied to the housing 2 and with the rubber plugs 36 being thereby compressed.
The waterproof structure shown in FIGS. 1A and 1B can collectively waterproof a plurality of the electric wires 7. However, an operation of fitting the rubber plugs 30 into the housing 7 is troublesome and in addition it is necessary to form the rubber plug 30 by replacing the mold in correspondence with the size of the electric wire and the number of the poles, raising the problem that the manufacturing cost becomes high.
Also, the waterproof structure shown in FIGS. 2A and 2B enables the performance of the sealing operation of the packings 34 relatively easily and can cope with the difference in size of the electric wires and the difference in number of the poles to some extent. However, as the packings 34 are only pressed by the holders 33, it is unavoidable that as shown in FIG. 4 gaps 35 are produced at side portions of the electric wire 7 between the packings 34 and 34, raising the problem that the waterproofness deteriorates.
Also, in the waterproof structure shown in FIGS. 3A and 3B, as the welding portions 37 are only two in number, i.e., on both sides of the housing 2, central parts of the housings 2 are deformed as shown in FIG. 3B by the repulsion of the rubber plugs 36, with the result that the gaps 35 are none the less produced as shown in FIG. 4, raising the problem that the waterproofness deteriorates.